Operations at the site off the southern coast, where the 6 825 ton Sewol with 476 people on board sank on 16 April, had been suspended since Saturday morning because of strong tidal currents and heavy swells.
Improved conditions allowed a team of 16 divers to access the submerged ferry in the early hours of Tuesday morning, but no bodies were recovered, coastguard spokesperson Ko Myung-Suk told reporters.
The confirmed death toll stood at 275, with 29 still missing.
The recovery teams are under intense pressure to retrieve the remaining bodies as soon as possible, and Ko said they would do their best to make up for the lost days.
But the grim work is taking its toll on the divers, who are reduced to groping for bodies, most of them schoolchildren, in near-zero visibility.
Park Seung-Ki, a spokesperson for the federal anti-disaster agency, said counselling and psychiatric help would be "actively provided" to any divers who needed it.
Of those on board, 325 were students from a high school on an organised trip to the southern resort island of Jeju.
Initial investigations into the disaster suggest the ferry was carrying up to three times its safe cargo capacity.
All 15 surviving crew members including the captain have been arrested, together with five officials from Chonghaejin Marine Co., which owned and operated the ferry.
The captain and most of the crew were among the first to abandon ship and have been widely vilified for leaving trapped passengers to die.
The government on Monday revoked Chonghaejin's licence to operate the route to Jeju, citing safety violations by the company and crew.
The Sewol's regular captain, who was off duty on the day of the accident, has told prosecutors that Chonghaejin "brushed aside" repeated warnings that the 20-year-old ship had stability issues following a renovation in 2012.